induced hypothermia

hypothermia

[hi″po-ther´me-ah]

low body temperature; it may be symptomatic of a disease or disorder of the temperature-regulating mechanism of the body, may be due to exposure to cold, or may be induced for certain surgical procedures or as a therapeutic measure. Hypothermia is a nursing diagnosis accepted by the North American Nursing Diagnosis Association, defined as body temperature reduced below the normal range for an individual but not below 35.6°C rectally (36.4°C rectally for the newborn). adj., adj hypother´mal, hypother´�mic.

Emergency treatment for hypothermia includes administration of warm intravenous fluid and use of esophageal rewarming tubes and special rewarming blankets. Resuscitation efforts such as cardiopulmonary resuscitation should continue until the patient is warmed to a normal core temperature; if there is no other change, the patient may be pronounced dead.

accidental hypothermia unintended lowering of body heat due to prolonged exposure to cold. Hypothermia is a chilling of the entire body, but the extremities can withstand temperatures as much as 10 to 15°C (20 to 30°F) lower than the torso, where vital organs are located. When the core temperature drops even a few degrees, physiologic changes can lead to fatal cardiac arrhythmias and respiratory failure. Persons most at risk for accidental hypothermia include the very young, the very thin, the very old, the mentally challenged or emotionally unstable, alcohol and drug abusers, and the homeless. Symptoms range from mild shivering and complaints of feeling chilled to loss of consciousness, absence of reflexes, and barely detectable pulse and respirations.

Prevention and Treatment. Accidental hypothermia can be avoided by eating high-energy foods, exercising when in the cold, wearing layers of clothing, and covering the head. From one half to two thirds of the body heat is lost through the head. For persons on a fixed or limited income, suggestions for avoiding hypothermia in a cold home must be realistic. Blankets and quilted covers that snap together to form a snug bag are alternatives to turning up the thermostat. A loose knitted cap worn day and night can help reduce loss of body heat. Persons who live alone may need help in finding another individual or agency that can check on them daily when the outside temperatures are very low.

The diagnosis of hypothermia may be missed if a clinical thermometer such as the kind used to measure fever is employed to determine the core temperature of a potential hypothermia victim. These thermometers rarely register temperatures below 34.5°C (94.1°F), while the patient's actual temperature can be as low as 30°C (86°F). Emergency departments should be equipped with special monitoring equipment that gives a true picture of the body temperature.

Once hypothermia is diagnosed, rewarming is indicated. Outside a medical facility the rewarming should be gradual so as to avoid respiratory and cardiac problems associated with rapidly sending cold blood back to the heart. The torso is warmed first by wrapping it in warm blankets or submersion in a tepid bath. Once the core temperature reaches 35°C (95°F), the extremities are warmed.

environmental hypothermia accidental hypothermia due to heat loss due to a combination of convection, conduction, and radiation to the surrounding ambient air.

induced hypothermia deliberate reduction of the temperature of all or part of the body; sometimes used as an adjunct to anesthesia in surgical procedures involving a limb, and as a protective measure in cardiac and neurologic surgery. The hypothermia may be continued only for the duration of the operation or it may be prolonged for as long as 5 days, depending on the reason for its use. See also hypothermia treatment.

Local Hypothermia. This is a type of refrigeration anesthesia restricted to a part of the body, such as a limb. It usually is used to produce surgical anesthesia immediately before amputation. Advantages include minimal risk of shock, lowering of cell metabolism, and elimination of the need for inhalation anesthesia in patients who are poor surgical risks. The part to be anesthetized is packed in ice or wrapped in a special refrigeration unit consisting of coiled tubes. Tourniquets are applied to the limb to inhibit circulation and avoid general chilling of the patient. The limb is chilled for 3 to 5 hours before amputation.

General Hypothermia. Generalized lowering of the body temperature decreases the metabolism of tissues and thereby the need for oxygen; it is used in various surgical procedures, especially on the heart. The core temperature is maintained between 26°C and 32°C (78.8°F and 89.6°F).

To induce general hypothermia, the patient is wrapped in a cooling blanket containing coils through which cold water or an antifreeze, or both, are circulated. The fastest method for achieving hypothermia is extracorporeal cooling of the blood; the patient's blood is removed through a cannula inserted in a large vessel, circulated through refrigerated coils and returned via another cannulated vessel.

Rewarming of the patient is accomplished simply by removing cooling blankets and allowing the temperature to rise gradually and naturally. In most cases regular blankets are used to maintain body warmth. External heat in the form of hot water bottles or warm tub baths, if used at all, must be applied with extreme caution to avoid burning the patient.

Patient Care. During hypothermia and the rewarming process the patient's temperature, pulse, respiration, and blood pressure must be checked frequently. Special electronic thermometers are often used so that the body temperature can be monitored at all times. In prolonged hypothermia, cardiac irregularities or respiratory difficulties may develop quickly; the patient must be watched constantly for changes in the vital signs, and any changes must be reported immediately. The skin also should be observed for signs of developing pressure ulcers, edema, or marked discoloration.

The patient should be turned at least every 2 hours, with special attention to proper positioning and good body alignment. Decreased secretion of saliva and mouth-breathing demand frequent mouth care. The eyes may need to be irrigated frequently and covered with compresses moistened with physiologic saline solution or artificial tears if the corneal reflex is diminished and eye secretions are reduced.

Intake and output are measured and recorded. An indwelling catheter is inserted prior to induction of hypothermia and is left in place until normal body temperature is established. This is necessary because urinary output is diminished during hypothermia. Fluids are given intravenously and the oral intake of food and liquids is prohibited because of depression of the gag reflex.

Shivering during prolonged hypothermia must be avoided as it tends to elevate the body temperature and increase metabolic needs, thereby defeating the purpose of hypothermia.

During the rewarming process the patient must be observed for signs of increased tendency to bleed and of gastric distention; these are common complications. After the body temperature returns to normal and becomes stabilized, the patient is allowed to progress to a normal diet and physical activities.

regional hypothermia temperature reduction in a limb or organ resulting from application of external cold or perfusion with a cold solution.

symptomatic hypothermia pathologic reduction of body temperature as a result of decreased heat production or increased heat loss. Hypothyroidism, severe blood loss with circulatory failure, and damage to the heat-producing cells of the hypothalamus can lead to decreased heat production. Prolonged exposure to cold, overdosage of antipyretic drugs, such as aspirin, and profuse sweating (diaphoresis) are some causes of increased heat loss and resultant hypothermia.

induced hypothermia

Any technique in which body temperature is lowered to reduce metabolic rates, oxygen demand, or organ damage. Therapeutic hypothermia has been used to manage stroke and traumatic brain injury, to alleviate fever or pain, and to improve outcomes in surgery or after cardiac arrest. Informally known as chill therapy. Synonym: hypothermia therapy; targeted temperature management; therapeutic hypothermia

CAUTION!

Potential complications include cardiac dysrhythmias, disorders of blood coagulation, infections, and injuries to or burns of the skin.

Patient care

In adults, the body temperature should be lowered between 90°F to 93°F (32°C to 34° C) ; in children, 91°F to 96°F (33°C to 35.5°C).

hypothermia

low body temperature.

Hypothermia may be symptomatic of a disease or disorder of the temperature-regulating mechanism of the body, may be due to exposure to cold, or may be induced for certain surgical procedures or as a therapeutic measure. Exposure to cold is well tolerated by animals except those that have poor peripheral circulation, e.g. cows with milk fever, animals under anesthesia and the newborn. Newborn piglets are particularly susceptible, but high mortalities may also occur in lambs during inclement weather and puppies deprived of warmth from the bitch. Even adult sheep may die of hypothermia if they are exposed to cold, wet, windy weather immediately after shearing.

induced hypothermia

deliberate reduction of the temperature of all or part of the body; sometimes used as an adjunct to anesthesia in surgical procedures involving a limb, and as a protective measure in cardiac and neurological surgery. The hypothermia may be continued only for the duration of the operation or it may be prolonged depending on the reason for its use.

neonatal hypothermia

a significant cause of loss especially in lambs born outdoors in changeable weather with a high chill factor combining low temperature, rain and wind and no shelter from the wind. Piglets are the neonates most susceptible to cold.

symptomatic hypothermia

pathological reduction of body temperature as a result of decreased heat production or increased heat loss. Hypothyroidism, severe blood loss with circulatory failure, and damage to the heat-producing cells of the hypothalamus can lead to decreased heat production.

therapeutic hypothermia

the application of cold to acute injuries induces vasoconstriction and limits edema and muscle spasm.

Although the Apgar score has not been helpful in predicting which infants will develop cerebral palsy, especially in the era of induced hypothermia for asphyxia, [12] it has been shown to be very useful in predicting survival in both preterm and term infants.

Temperature Modulation Therapy for Ischemic Injury Numerous scientific and medical articles have described the usefulness of temperature modulation, such as induced hypothermia (cooling), which is designed to protect endangered cells, prevent tissue death and preserve organ function following acute events associated with severe oxygen deprivation such as stroke or cardiac arrest.

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